Australia 75th Anniversary Of T P I

This Australian stamped envelope was in the discount box at my local stamp show. Unused and unaddressed, it clearly states, "75th Anniversary of the Totally and Permanently Incapacitated Pension." What I find interesting is that the "Stamp" is albino-style, and since I had never seen this envelope, I was wondering if it is completely normal. Also, any information on TPI in general would be appreciated.

Partime,
Yes, that is how they were issued.
More information can be found on TPI here:
https://tpifed.org.au/

Thanks so much for the additional information.