The document you found is something I created to try to figure out and list E-plate numbers for CHPs. It's not complete, it's a work in progress. The idea to cross check E-plates and VINs was not mine but I ran with. The idea and the additional work I have done in that document has helped us figure out E-plate numbers for some CHPs.
Here is the direct link:
http://foxchassis.com/files/SSP/CASmogCertificates.xlsx
I have a bunch of other documents in the parent directory:
http://foxchassis.com/files/SSP/
If you are certain that your CHP's unit number was #9186 then the original E-plate was probably E389186, and not E899186. Reason why you didn't find any info for E389186 on the CA smog history site is probably because the info is too old for when it was in service. And yes, E-plates are reused.