How many LO (half-stealth) planes are around there?

We often debate at length about airborne radars respective performances but what about the receiving end?

Putting a brand new Aesa or Pesa radar on a legacy plane is surely a big improvement but it would risk to fall short (and costly) if no adequate measures are taken about RCS reduction.

On the other end also these kind of modifications have their costs and above all they require a lot of time to be tested and sometime they are just not convenient to implement for plane about to be retired in a few years.

So, it’s possible to get an idea of what percentage of the birds of a given airforce has received such type of improvement? and at what length?