I got the V5C's for my CB72 and Bomber last year from DVLA and immediately declared SORN as I got a warning letter telling me I would be in bother if I didn't. I checked a few weeks later and still not showing as being SORN so I tried again. Each time I did it I got a DVLA confimation email that it had all gone though OK. I looked on DVLA weeks, then months, later but still not showing SORN on both bikes. Called DVLA on another issue today and asked about the SORNED bikes and seems that if the vehicle was last taxed before SORN came in it will not show on the Vehicle Enquiry on-line but shows on their internal system.
So we keep looking up a bike and thinking it's long gone but could be fully restored and SORNED but never taxed since pre-SORN.