Background: I was applying for grad school last year, and asked my professors for a lot of rec letters(likely 15 programs which made the work really tedious). They kindly agreed and send all the rec letter much earlier before the due date, and the outcome is really good, I had been admitted by almost all the excellent universities which I thought I won't had much chance, so I suppose my professors' recommendation helped a lot and I am very grateful.
However, the problem is, due to complicated reasons I had to reapply this year, and I'm not sure whether it would be appropriate to ask professors who already helped me once again since I already troubled them too much last year. And I didn't contact them after I send them a thank you letter which made me feeling like the only thing I did after graduate is keep asking rec letter from professors. I could find enough rec letter from my intern supervisor since I had graduated for a while but my friends told me universities really value the rec letter from undergraduate professors so I better at least have one. My current plan is that I would ask them if they still have the rec letter they wrote for me last year and if so, I will awkwardly ask them again. I really appreciate what my professors already done for me and I really don't want trouble them. It appears to be a very hard time for all universities and professors because of the CVOID situation, so I'm not sure if I should even bother them at this point. Please let me know if my plan would be culturally appropriate or not. I graduated from an american college if it matters.