Reserve question here - how does pay work on a carry-over rotation? I had a CA tell me to be careful b/c the last carry-over trip he did on res all of the pay/credit went towards the later month.

I have 2 days of availability at the end of Jan and I know they are going to fly me. Currently I'm just below being 'full'. I also have 6 more days after that going into Feb. Based on what this CA told me I'm worried if they give me a 4 day carry-over all of the pay/credit will just go towards my Feb res guarantee and I will have worked to within .5 hrs of guarantee in Jan for 'nothing'. Is this crazy? I couldn't find anything about carry-over/asterisk rotations on res in the PWA. Thanks.