Australian Postal History Puzzle

I've been wondering for a long time what this unusual postal corner is about. The stamp on the right has been covered with some kind of thick protective transparent adhesive on which the inscription BATCH 1203 is printed in red.

I have no idea why this would have been done, but the thought occurred to me that it might have been a post office experiment of some kind.

Has anyone seen anything like this before?

These staps were designed by Wayne Rankin; Printer: SNP Sprint
It is part of Issue 6, Part 2, Nature of Australia, there were 4 stamps in this release (all 50c), the Orange-thighed tree frog (Litoria xanthomera); the Green-spotted triangle butterfly (Graphium agamemnon ligatum); the Yellow-bellied sunbird (Nectarinia jugularis); the Striped possum (Dactylopsila trivirgata). Nature of Australia has had a number of issues with many parts; however I don't know about this Batch 1203.

This might seem like a dumb question, but, is the cancellation under or over the thick transparent adhesive??

If it is over, I am wondering if this was applied by a post office employee to mark some designated 'batch' of mail to go to a particular area. I am wondering if so many covers would be process and this was done for bulk mail. I also noticed that this might be a type of 'parcel post' cancel? Again, if so, then maybe this bulky package was designated a 'batch' number for specific sorting purposes?? Wild guesses on my part.

Chimo

Bujutsu

Hi Bujutsu, I think that's actually a very apposite question. The cancellation is over the adhesive, so the adhesive was placed over the stamp prior to posting. Why just one stamp and not both I have no idea!

Hi jimjamtwo

This is also what makes me think it was a type of sorting sticker. If that is the case, they would only need to cover only one stamp and send a bundle off to the different locations in bulk. Again, just a guess.

Chimo

Bujutsu