What is cap count what is its current value?

By definition cap count is number of application approved plus unprocessed. More over, there is priority processing which overrides all normal requests which are still unprocessed. How do you figure out a reliable cap value when you dont know how many are going to be rejected among unprocessed?

I think unless you receive a receipt number, you are not sure if you are within the cap or not.

Am I making mistakes on mu judgement?

A good way to check this is if your USCIS filing check is encashed , they you are in. Even if it takes longer for you to get the receipt

Yes, Receipt Number is the ultimate confirmation that you are within the cap limit. As the other answer suggests, checking the status of cheque encashment is an indirect way of identifying this.

Regarding reliable cap count - the rejected application count will not be deducted from the  current quota's cap count. Those numbers will be used in the next year quota.