The POH /AFM are usually the best source for numbers .
The difference between IAS ,CAS and TAS in GA are so small that it is really and truly Academic.
A-Question may arise as to “when “you might choose to use a speed other than flight tested and approved by the sky gods .
Gusty conditions and Cross winds you might want to add some airspeed to give a little bit more control .
Aircraft might be damaged and it starts to do weird stuff when you slow down . I had the top corner of a windscreen depart in a spin . The slowest speed I could get and still have pitch control was 90 KIAS , so I landed at 90 . I was surprised how quickly it stopped on the ground . I was expecting to go off the end . But the drag from the big hole slowed the plane in under 2000 feet .
Changes were made to a few aircraft window seals after that flight .
General rule is you never want to be slower than the POH recommended speeds .I flew with a guy who used really slow speeds for short fields , but you would never deliberately land somewhere that was so short you could not get out again . Almost a helicopter approach . I Showed him how to land a 172 in 150 of ground . It was fun but the slightest turbulence and it would have got expensive real quick . Pointless exercise as you need at least three times that to get into ground effect for departure in a light plane into wind .
Many students get the airspeed covered in the circuit to prove that the airplane can be flown without the airspeed indicator working , you just have to give yourself more room and do not rush the approach .
Time to Fly