Yeah, I recently upgraded to Mileage Plus Explorer Visa Signature and they said new rules and regulations only allow for credit cards to be converted after one full year of having the card. Also all Visa Signatures require a minimum CL of $5000.
I got freedom non visa sig a few weeks ago from a PC from SWRR visa sig 6k limit was told to call back after 93 days to get sig. Was told initially it was to be asivas sig. Just my experience.