However, there are readers that use a "scan range" approach. They don't employ any intelligence, but instead continuously adjust their own operating frequency essentially scanning through the entire operational range looking for tags. This is the "shotgun" approach to RFID, in which the entire frequency range is dominated by a single device. By hitting every single possible frequency within it's configurable range, the reader doesn't care if there is another device operating at 912.68MHz, it will bulldoze right through that frequency range every few seconds (or less). While the reader is using 912.68MHz to scan for tags, it will be interfering with the other device using that frequency, and it will not likely be able to talk to tags very well at that frequency. No matter though, the reader will just hop to the next frequency and try again. It's a very "dirty" way to operate a reader.

There is one positive reason for a frequency scanning UHF reader, and that is in situations where there are no other devices operating in the 900MHz spectrum, but there are other interference issues like metal or liquids in the area, either from equipment or walls or whatever else there might be in the way. A frequency range approach helps mitigate these interference issues by trying many different frequencies, which all behave slightly differently when propagating through the same space and bouncing off the same walls. One wall might contain materials that reflect 913.456MHz but pass 910MHz just fine. A metal shelving system might interfere with 912MHz but be fine with 915MHz. It's hard to tell what kinds of interference issues might cause reliability problems in warehouse or manufacturing environments, so being able to simply scan an entire range of frequencies to get the maximum range and reliability out of your reader can be a good thing when used in controlled situations.

I mean the readers I have got the option to change working frequency from 902MHz to 928MHz. I can either select a range for e.g. 910MHz to 915MHz or single working frequency for e.g. 915MHz for a reader so I wanted to know the difference between these two.

Will using single frequency increase signal strength and reading range of reader?

I'm sticking to the idea that to speed things along, you should try to get a spec doc from your supplier for the tags you're reading.

Hmm, did you get each of those different TIDs using the same reader settings, or were you changing settings between each read?

Either way, I think your best bet at this point is to see if you can contact your supplier to get a spec document for the tags you're using, complete with a memory map that details which memory blocks contain the TID and what the nature of it is.