Can somebody tell me what is the real difference between the different models of A-02 DLE ignitions? I noticed all of the model A-02 come with a type "# (from 1 to 4)" printed on the front and a sticker at the back saying "To be used only with the DLE xyz model), so it looks to me that is "customized" for that particular model of DLE engine

Right now I'm using a type #1 (meant for the DLE 55) on an RCGF20cc engine, the engine starts very easily and accelerates just fine, the only problem is I'm getting a maximum of 7400 RPM at the leanest HS needle point. Do you think is because of this type#1 ignition and I should try one meant for a 20cc engine instead of the one for the 55cc? on the other hand, I noticed that RCEXL only produces one model of ignition that is supposed to be compatible with any DLE engine

All of those different tags confuse the issue. I can't really answer your question because the various companies are very tight lipped. I can tell you the only DLE ignition I have found to be uniquely different with regards to performance compared to others produced in the same time period was the old A-01 #4 that was provided with the early DLE20 engines. That particular model had a very strange advance curve that made getting a consistent idle speed almost impossible. The later A-02 version resolved the issues. I have interchanged ignitions between various DLE engines and have noticed no differences between how any of them performed. Other than the angled cap versions and some that have longer plug leads, I find they all work the same and interchange. If you buy a generic RCexl ignition, there is only one to choose from. An exception might be various RCexl ignitions marketed under the same # might have different operating voltages depending on when they were produced.

You might note that DLE parts that are identical between their various engines are marketed with different part numbers for each engine. This might carry over to their ignitions.

If your engine is timed properly I doubt the ignition is the cause of any low RPM problems.