He managed to convince Zed and got his job as Agent M.
- Or maybe he just got kicked off the planet, or got tired of waiting and just went home.
The Liberty Island neuralizer had secondary effects built in.
Primarily, erasing undeveloped film and not having to look directly at the birdie (possibly not even having to be in the light itself, but only within a certain range which is lessened but not blocked by cement). It is likely that, aside from being lower-powered, the personal neuralizers are intentionally nerfed
versions of this original-design neuralizer. Unfortunately, this means that any MIB agents within range who had their glasses off (anti-neuralizing field generators in the earpieces) lost their memories of that time as well, and that the MIB will have to find a new way to deal with flash memory storage for digital photographs now that it's become much more common.
- The MIB doubtlessly wouldn't allow flash memory storage technology to be released to the masses until they already had a guaranteed way to alter it.
Serleena ate Scrad and Charlie.
The last we see of Scrad and Charlie is the fight scene in Jeeb's basement, where he says that Serleena was going to kick his ass if he failed to take down J & K. Now nothing in the ensuing fight scene implies that he died during it. So what might've happened is that after he lost the fight he returned and reported his failure to Serleena and she had a You Have Out Lived Your Usefulness
/ You Have Failed Me
moment and devoured him/them. We already know that eating males is one of her preferred ways of killing them, so it's not too much of a stretch to say she did that to Scrad and Charlie. Theyre absent for a good chunk of the movie after that fight scene so she might've digested or regurgitated him/them afterwards, explaining why she didn't have a Balloon Belly