You could be doing it forever and not be paid for it - my boyfriend of 3 years (we met when he started at my store and I trained him lol) worked as sort of a combo BR Day/Pfresh TM in our Pfresh store, mainly pulling and backstocking pfresh items. Right after the pfresh remodel, the CTL taught him to do most of the things PA's do, including TPCs and ordering. He did this very well and trained numerous other TMs in pfresh. Then it was time for our store to hire a PA officially - he applied, interviewed and did not get the job. What he got was this - a lazy person who knew nothing about pfresh getting his promotion, and then he had to train that person to do the job he had been doing! Imagine his frustrations...
Now with all that said, he didnt have the best attitude because he had a hard time accepting the way Target does things, but fast forward to a couple of years later and he was finally made a PA and is doing a stellar job with a CTL position lined up and in his sights. So if you're willing to stick it out and gain some trust and support from the management, you may be able to turn your unfortunate situation into a good springboard for a later promotion by wowing them now with how you handle your extra responsibilities.