I've had it go both ways as well. Smaller museums being more willing to engage in a discussion in my experience. It also helps if you can provide a few references and sources for them to pursue.
The last one I got a positive response on was a small regional museum which was exhibiting a 19th century kaskara as 15th century Spanish! They were actually very receptive to being contacted as they don't have any specialized staff and were planning to change the labeling last I heard.
If nothing else, it gives peace of mind I think to at least be able to say I tried to let them know if there's something obviously out of place.
