That was the first observations I made, using extract.
Later I found out that the solubility actually depends on the MCT oil composition and also on the presence of waxes. The limit of the pure CBD Isolate in the pure MCT oil I use is ~33% At room temperature (22°C). It can be increased to ~47% using hemp waxes (maybe higher). It gets 5-6% lower in other kind of oil such as olive or hempseed. The more linoleic acid the less it is soluble. Thus tuning the MCT oil C8:C10 composition may also allow to increase the solubility.
Solublity apppears also a few % lower for CBG.
I have not tried to find the limit for CBN. It is at least as soluble as CBG.