If Claudia Wells Came Back...

I suppose that's true. If they hadn't refilmed the beginning, then Doc wouldn't have had a new reaction to Marty asking if he and Jennifer became "assholes" in the future. In Part 1, Doc answered right away. But in Part 2, he thinks about it for a second.

https://www.quora.com/Had-Claudia-Wells-been-able-to-reprise-her-role-as-Jennifer-Parker-in-the-Back-to-the-Future-sequels-would-they-have-still-refilmed-the-ending-of-part-1-beginning-of-part-2-to-accommodate-Michael-J-Fox-and-Christoper-Lloyd-having-aged/answer/Mick-Carlovski?__filter__&__nsrc__=2&__snid3__=1880500884

More than likely they would have done for a number of reasons not limited to continuity.

For me, the most compelling reason that they would have reshot the scene is that the original footage they shot is already being used in the first film. It was shot on film in the 1980s, and with the exception of special effects shots, the standard procedure is that the processed film that was actually in the camera when they shot it is ultimately sliced up and reassembled into the master negative from which all subsequent copies (for release) are taken directly. If they wanted to re-use the footage from the first film, their choices would be to remove that section from the master negative (permanently damaging the first film in the process—it could never be archived or restored), or they could use a copy. With film, making a meaningful copy in this way would add two extra generations of duplication artifacts which would seriously lower the quality of the final product. So they’d just reshoot it.