Jose Bonaparte was an usurper and all his acts were considered null and void.
On the contrary, Amadeo was a legal King. Noble titles and even Knights of the GF created by him were considered legal.
About carlist titles you have explained it. Franco recognised them, but it was not automatic. Their holders had to go through a legal procedure to have them recognised by the State.
King Juan Carlos never challenged decisions taken by Franco. If those titles were legal according to the law in 1975, why abolishing them?
The previous thread I began below was about the current situation of Spanish noble titles given during Franco era, but while doing some research on that topic I came across some other issues related to titles in Spain. These are truly more obscure questions - but I'm interesed in any answers even if general points. 1. Noble titles granted by kings who occupied the Spanish throne just for a short time and were not Bourbon dynasts - so, Jose I (Bonaparte), in the early 19th century. Did King Jose grant titles during his brief 5 years, and if so were those all erased when the Bourbon kings returned? 2. King Amadeo I (Savoia), in the later 19th cent. Did Amadeo grant any Spanish noble titles during his period on the throne - and again, did the Bourbon monarch who followed him erase all of those? 3. Carlist titles - I'm not even sure who granted these during the Carlist wars, but they existed until the Bourbon king defeated the Carlist pretender, then apparently he erased them, but then again when Franco came into power he restored these. But, strangely, it seems King Juan Carlos had no problem with their existence (even if his ancestor had nullified them), and likewise his son Felipe VI and PM Sanchez and his govt. consider this "too long ago to really matter"? But hopefully Manuel is reading, and can correct any facts I have wrong here, and provide some answers on 1 - 3.