I would guess it is likely that one might work better than the other at least one might be preferred. Sounds like yours was fairly successful, right? But then again can't really say for sure without trying both, and it is really difficult to say without lab equipment and testing, and actually knowing which conversion rate might have happened in your double decarb method. Or if it were both.
You did mention that you noticed a slight THC buzz right? I have to wonder if the other route was taken (THCA - CBNA) might give you more what you are looking for as the THCA would never have the chance to become THC, and therefore the undesirable trait in your case. The only question then would be what sort of decarb is best for CBNA to become CBN. And then of course the same for converting THCA to CBNA without accidentally making some unwanted THC out of some of the THCA.
You did say that was batch one of many? All I can suggest is to keep detailed notes on each batch of exactly what you did, and the results. Hopefully at some point someone can get one of these conversions tested either with TLC or a $60+ HPLC test. TLC seems to be limited in its the detection and differentiation between the different acids. Then again HPLC analysys sheets rarely show the ratio of acids to active cannabinoids other than THC and CBD. Might need a special request with the lab doing the HPLC in order to get the extra detail on these secondary CBN/CBNA compounds.
@cannabineer Do you remember at all which conversion route you were doing in the lab? Did THCA and/or CBNA come into the picture, or was it a straight THC-CBN conversion?