I cant say that I blame you for using steel cased ammo for your LCP. Its a 380 and those are expensive to shoot, I got rid of one for half of that reason. The other half was it didnt want shoot hp ammo.
Your question: I have shot from cheap to terribly expensive ammo in my guns(ruger p95, sr9c). They all still shoot and I cant imagine your lcp being damaged by the small amount of steel cased ammo youve used. Im sure that theres reasons why some say not to shoot them(post above), but if its what you can afford Im sure your practice is more important than the tiny amount of damage done. MAYBE after a few thousand rds you might start having problems, MIGHT. I have complete faith in Ruger though.