You cant fix a ceramic plate once a bullet has fragmented it, you discard it. So yes, pretty realistic that you cant sow new kevlar on..
You sir, are internet hero.
Though I do wonder why they don't just handwave it being "unrealistic" since it's a pretty essential need for any player. And, I mean, it's fairly common to just slip a new trauma plate under your IBA/IOTV or remove them entirely when not needed among service personnel. Hell, since replacing the whole thing is more expensive than just the compromised plate a lot of people do sew/patch over the holes in the fabric itself.
well i also tested some things in fixing equipment ... i also tryed to put some armor inside a workbench (northern hangar in drassen airport) and wait some hours but this also didn't work ^^" well its not like JA2, BA wont reward experiments