As it says at the top (of the gameplay) it says you need to clear out 25 lines. The quickest way for NES Tetris is to use the field to your advantage as most of the layout is done for you. It's just convenient that it ends with an All Clear.
Good find! It desyncs after the Georama fight and not for the reason you think -- there is now an extra lag frame on 47406. Even after inserting another frame there, the bee at 50437 now has a completely different initial trajectory. Position and subpixels are reset between screens, but the game has oddities with timing that I could never work out, even when RNG (0xB562) is controlled.
Something interesting with this game's in-game timer is that it doesn't actually track time in minutes and seconds, but frames. As in, when the game displays 0'14"65, for instance, it's actually 1465 frames, not 14.65 seconds.