It's surprisingly difficult to obtain information on interline agreements of any kind. I know, I tried in a previous existence. The IATA MIBA publication provides some data but there are a range of agreements outside that publication. Even if you start asking airlines for the data (and I had a very valid reason, it was even something airlines had asked us to do) trying to discover the person who holds that data is difficult. Then you run in to maintenance problems when that person moves on and fails to brief their replacement.
I agree that it's a stupid situation but there its is.
I would suggest that it's probably a reasonable assumption that within a given alliance (Star, oneWorld) interlining exists but other than that it's hit and miss.