Yes, converting .lvl to .ini isn't as straightforward as a mass conversion and hoping that everything will be correct in Superlemmini. As I already pointed out, I still had to check everything for Deceit's Lemmings, and as it turned out there were still issues even though the conversions to .ini went fine: fall distance doubled the default, non-working steel on some levels, some exits too low/too high, and some non-working traps. Once I took care of the issues, then I released the conversion of the pack. Yes, it can be annoying to check everything, but it's a good practice to check to make sure everything is fine before release.
Most importantly, as eric has mentioned, Lemmings Reunion was, by far, the most difficult pack to convert. It took him a very long time, almost 1.5 months IIRC. I can attest to this, as I have read his copious notes on every level he edited. I provided input, assistance, and replays wherever I could if there were any I thought would be of interest for him when converting/editing. Also, there are some styles that didn't play too nicely, such as the L2 and Castle and City and Sega tilesets. And of course, there was also the annoying mild slopes to bash which doesn't work in Superlemmini, as well as climbers being able to climb past builder walls, and climbing through terrain that they shouldn't, such as crosses from the Dirt tileset. Now that Tsyu has returned after so long, perhaps he can tell us if these issues were intentional or if he agrees they should be fixed.
Needless to say, make sure to take your time, as converting any pack to Superlemmini takes a while. Doubly for Nepsterlems, since it has double the amount of levels that Deceit's Lemmings does and therefore there are way more things to check. However, as this was the first Neolemmix custom pack you converted to Superlemmini, you still did great for a first attempt. It's likely that you simply weren't aware of the issues that can result from converting.