Adobe Captivate version problem

I'm sorry but although they both are labeled as CP2019 versions, the compatibility between 11.0 and 11.5 is the same as for full version releases. Too much added features in 11.5 are the cause that you can open a 11.0 file in 11.5 and upgrade it, but not the other way: it is impossible to open a 11.5 file in 11.0.

We have developed a course using Adobe Captivate 19 v11.5.1.499, but later we tried to open it in v11.0.1.266 and we are unable to open it, we have requested from client the source to be open in v11.0.1.266.