Missing devices from switch inventory report

I've been trying to create custom report of all (mostly Cisco) network devices in my LAN.

Query rules are easy:

Usergroup (my own custom property) must contain "network" (there is different groups that include network devices, and they all have that text in their value)

AND

City (another custom property) must be "Mycity"

AND

To get rid of serials that are not real serials, value should start with "F". (in some switches there are many different serials under "physical entities" class, mostly in form 0108082026136929, as real Cisco serials begin with "F".)

That should have done the trick. But...

1. Firstly I cannot get any device information about WLAN AP's because they are controller based. That's probably a thing that I cannot do much about, because AP's are monitored only with ICMP... So I have to get them from WCS report, export everything in Excel and combine in there. Btw, in NPM 12.0.1 Excel export doesn't seem to work with Chrome. With IE I got it work.
2. But a critical problem is that some switch serial numbers are missing. It shows in NPM node view page, but doesn't appear in reports. I only got names, IP's and descriptions, but serials are the main reason I run the report in first place. I've made universal poller to node view page (entPhysicalSerialNum) and even that finds serials for all network devices, but the report doesn't!
   1. For example two identical 2950G switches in same network... Same IOS, same model, serial begins with "FOC".. but the other one doesn't find serial and other does!
   2. All switches from another subnet are missing serials! And again, it exits in node page. Also model and software version is missing for those switches! Could be something common maybe? They are behind firewall, but SNMP ports are permitted, so all the same information should be in there, as for switches in another side of FW. Am I wrong? They are also behind NAT, can that cause problems?
3. Also some of switch software revision (IOS version) fields are empty. That could be because very old IOS versions in 2950G's ( 12.1(19)EA1c) because version 22 seems to show ok. Any other place where I could get that information from? It does show in description field, but that text is so long that I don't want it to reports...
4. And finally, report doesn't seem to find Catalyst 6500 and 3750 at all. I would also need serials for all installed 6500 module cards, is that possible to get in report?