Well done! I remember watching this anime back then. ;)

@Yawackhary
I think you might be refering to Liza from the first TV Special "Bye-bye Lady Liberty - Crisis Averted!", as she looks relatively close to the girl shown, as well as her own robes in the climax, and the special's overall artstyle closely resembling that of "Lupin vs. the Clones/Secret of Mamo"

As for that other car present in the last slide, I think it might be a Citroën 2CV, which was one of the cars that was used in Part 1, alongside the Mercedes Benz SSK and the Fiat

They are all references to the series in some ways: The ending of The Castle of Cagliostro, describes the ending to The Mystery of Mamo (even though Fujiko seems to have been replaced by random TV Special girl), the cover/poster of The Castle of Cagliostro, Maki Oyamada and Lambda from the final episode of Part 2, Lupin discovering Pycal's trick from The Man That They Call a Magician from Part 1 (and technically the 14th chapter of the original manga too since it was an adaptation) and a group picture of the Lupin gang.

First that I thought that it might be from Part 1 judging by Fujiko's design but the vehicle isn't the Mercedes Benz SSK or the Fiat 500... Hmm...