[isthisLOL?]

To my knowledge ST02 was Ayumi's first tour filmed using HD cameras, but not all cameras used were HD, it was a mix(obvious even when watching the DVD because the image of the HD cameras is still a bit sharper), her first concert filmed fully in HD was AT05.
However, that doesn't have to mean anything when it comes to PVs. It depends more on if they were recorded on film or digitally. Concerts are generally filmed digitally since the pure amount of cameras makes digital recording a LOT easier, faster and cheaper. Film would be impossible to use live. Film can be mastered at 1080i Full-HD in incredible quality as long as the originals are used but most digital recordings of that time were not in HD. My guess is that if she recorded digitally(it may be a mix, too) filming PVs in HD didn't begin any earlier than 2003, if she began then. Especially the PVs for Love Songs show film grain(but that may be digitally inserted to create an effect and not real) so those probably CAN be mastered at Full-HD in great quality while the Five PVs seem to be digital and in true HD.

Someone has to watch making-ofs and look for the types of cameras used lol