VB6 - releasing only a few DLLs that are heavily dependent without breaking any links

I need to release a few changes to selected DLLs (simple changes inside methods - nothing that breaks compatibility according to this )

Thus, the generally accepted method is to maintain old DLLs in a separate shared directory and compile them when creating new DLLs using binary compatibility installed in the old DLL set. This is done so as not to change the GUID when registering new DLLs. These GUIDs are used as links in other DLLs that I did not break at the time of release.

Now, when I try to create some new DLL, I get a warning: "The binary compatibility DLL or EXE contains a parameter type or return type, the definition of which cannot be found." I’m sure I didn’t add anything to violate the binary compatibility rule (no change in signature, public methods, variables, etc.). Am I a noob without checking something basic?

With a kiss on my head in the morning. Any help is greatly appreciated.

EDIT: If there are any changes to my signature at all, is there a way I can know without comparing the code?