Thanks so much ssprengel for taking the time to reply - here we go (long post ahead!):
JACK & JILL'S WEDDING (Parent Folder) (typically 40GB in size initially 90GB in size when all edits are completed)
-Family Group Photos (Subfolder)
-Wedding Decor (Subfolder)
-Getting Ready (Subfolder)
-Church (Subfolder)
etc
Here's a sample workflow:
You'll see Three devices that are involved: Main Computer, External USB 3.0 HardDisk and Retoucher's Computer.
Wedding Photographed - multiple memory cards put in three different card readers plugged in to Main Computer.
1) In LR - File > New Catalogue > Jack & Jill's Wedding created.
2)Import, all three memory cards selected (under Devices) and set to Import & Convert to DNG.
3)The entire Jack & Jill's Wedding Parent Folder with Catalogue (and previews) is then copied to External USB 3.0 HardDisk .
4)The entire Jack & Jill's Wedding Parent Folder with Catalogue (and previews) is then copied to Retoucher's Computer.
5)Retoucher opens Jack & Jill's Wedding Catalogue and organises images into subfolders (eg Family Group Photos, Decor etc) within LR.
6)Retoucher stars useable images with 4 stars.
7)Retoucher labels 20 Family Photos to edit as Blue.
8)Retoucher makes Develop Edits (Highlight , shadow, clarity, Lens Correction etc) on 10 photos, Edits 5 of these photos in Photoshop via Lightroom's Edit-In option and saves them from Photoshop in the same Family Photos folder.
Thus we have: 20 Family Group Photos as DNG , (10 of these have LR edits) and 5 Uncompressed 16-bit Tiff Photos. Of course 5 of these Edited-Only-in-LR DNG's are redundant as they've been further edited and saved as Tiffs.
9)We still leave them there though and unlabel them blue to no colour to avoid confusion.
In Total , in the Family Group Photos SubFolder we now have 25 images - 20 DNG, 5 Redundant DNG and 5 Tiff.
10)Retoucher then selects Attribute > Blue.
11)Retoucher selects 15 DNG files and 5 Tiff files.
12)Retoucher then Exports these 20 files as uncompressed Tiff 16 bit images to a new subfolder: "Family Photos for Editing at Acme Photo Company"
13)Subfolder "Family Photos for Editing at Acme Photo Company" is then copied via Windows to a USB or CD and send over to Acme Photo.
Acme Photo Retouchers don't use Lightroom sadly so they load the images directly into Photoshop via Bridge or ACDSee or just plain ol Win Explorer.
14)Acme Retouchers do the needful and save these images as 16 bit Uncompressed Tiff images with the suffix '-edit' eg 'JJ-101-edit.tif' , put them back on the CD/drive and deliver them back to us.
15)Retoucher then moves (via LR) all the 25 DNG & Tiff images into a Sub-sub folder "Family Group Photos - Old Versions"
16)Retoucher then Selects "Family Group Photos" right clicks > Import to this folder > Imports (copy) the 20 Acme Photo Edits (Tiffs) into that folder.
The Overall folder tree looks like this:
Jack & Jill's Wedding Parent Folder.
Parent folder contains multiple subfolders including our "Family Group Photos" subfolder.
"Family Group Photos" Subfolder contains two Sub-SubFolders 1) "Family Photos for Editing at Acme Photo Company" and 2) "Family Group Photos - Old Versions"
"Family Group Photos contains: 20 Uncompressed 16 bit Tiff Images.
"Family Photos for Editing at Acme Photo Company" contains: 20 Uncompressed 16 bit Tiff Images.
"Family Group Photos - Old Versions" contains: 25 images (20 DNG and 5 Uncompressed 16 bit Tiff Images.)
17)Retoucher will then perform additional edits on the 5 -edit Tiff images in "Family Group Photos" Subfolder in LR Only and 5 in LR & Photoshop. He will save 4 of these tiffs overwriting the files in the Family Group Photos folder but save 1 (JJ-101-edit.tiff) which has extensive edits so he saves that as "JJ-101-edit edit.tiff".
18)Retoucher will then move "JJ-101-edit.tiff" to "Family Group Photos - Old Versions" folder as this is now redundant.
This is where it gets even trickier:
19)Retoucher will then use FreeFileSync Program to mirror Jack & Jill's Wedding parent folder on Retoucher's Computer with Jack & Jill's Wedding parent folder on External USB 3.0 HardDisk One. This updates all folder contents including LR Catalogue and edited tiffs such that there are now two idential copies of the same folder/catalogue on Retoucher's Computer and HardDisk One.
20)FreeFileSync Program is used again to mirror Jack & Jill's Wedding parent folder on External USB 3.0 HardDisk with Jack & Jill's Wedding parent folder on Main Computer.
This updates all folder contents including LR Catalogue and edited tiffs such that there are now three idential copies of the same folder/catalogue on Main Computer, Retoucher's Computer and HardDisk.
21)I now use the Catalogue on Jack & Jill's Wedding parent folder to view the edits and changes are satisfactory and use my computer's awesome powers to export the Tiff images as Hi-res Jpeg for delivery to the couple (along with all the other scores of images from other folders etc).
The folder Jack & Jill's Wedding is now ready for Archiving which brings me back to my original question: There are a total of 46Uncompressed 16-bit tiff photos spread accross three folders "Family Group Photos" subfolder and it's two sub-sub folders.
22)I want to turn these into 8bit-Zip compressed Tiff images to save space. (Don't forget this is just an example - in reality Jack & Jill's Wedding will contain hundreds of tiff photos - the family group photos alone can end up at 100 plus a dozen other weddings!)
Additional Note: Many of these Tiffs will also contain layers. I'd like to preserve the layers when compressing.
So there we go - phew!
Kudos if you've managed to make sense of this - suggestions for the initial problem and workflow issues welcome!