Both Flexi and Suvidha are same Suvidha is only the name of the train while Fares are Dynamic/Flexi. Suvidha Train was only one which I remember was Santragachi or Guwahati train which doesn't exist and is stopped. Only one more Suvidha came is from Ernakulam to Chennai or I think Coimbatore-Chennai Suvidha which was withdrawn later.
Special Fares are like.
12625 from TUP-NDLS charges are Rs.2250-2300 approx of AC 3 Tier.
When...
more... 04425 was Started as AC Special it was successful and was operated for 1 year.
The cost was only Rs.2500 from Tiruppur to New Delhi.