I personally know only very little coding (just your friendly neighbourhood game designer and a fantasy-writer ~ Not some programming-savant despite my background with a degeee in IT-Engineering and as someone who has also studied game-coding officially in school ), so I can't possibly tell you why there either were no invulnerability-frames at all or if there were, they weren't long enough. Also because I haven't seen this game's code personally
Glad you were able to find it appealing and worthwhile though, thank you! ^_^