PVA Quality

So I was at an exhibition at the weekend and I was warned by a fellow artist about the quality of some PVA and that it can deteriorate over time. I think though that she was using it neat and the risk was with it yellowing over time but as I use it mixed with stucco I think the risk of it ruining anything is very low. I have used it for over 5 years and have not experienced any problems with it. However, you do pretty much get what you pay for with PVA so I would advise going with a good quality brand.