Help please. Can anyone explain these numbers from population surveys?

I am a country person who enjoys bird spotting, but I could never be described as an avid bird watcher, although I am trying to photograph as many different birds as possible within a 2 mile radius of my home in South-west Durham [89 so far], and a great deal of my time involved in walking around my area is spent looking at and photographing birds.

A few days ago, there was a post on 'All creatures' concerning Magpies that promoted a great deal of discussion. Trends in bird populations were brought into the arguments and I asked how accurate and what percentage of the country is covered by these surveys. I was not trying to de-value these surveys, as I feel that any information about populations can be useful, I was simply asking how they were carried out and what areas of the country they covered.

On Saturday, I took my usual morning walk and photographed 4 small birds, high in an ash tree, that I did not recognise. Returning home and editing the photographs, I discovered that I had been observing two pairs of crossbills. As I thought that this information would be of interest to bird watchers, I started to upload a picture to the 'Bird Guides' site, only to have it rejected as the crossbill is a Schedule 1 bird.

This started me wondering about the Schedule 1 list - something that I had vaguely heard about, but something about which I knew virtually nothing.

Looking at the birds on the list, four species in particular caught my attention, cross bill, willow warbler, yellow hammer and yellow wagtail. The crossbill is on the GREEN list, although apparently none were recorded in England in 2010; the Willow Warbler  [1354 recorded] is on the AMBER list and the yellowhammer [ 1141recorded] and yellow wagtail  [153 recorded] are on the RED list. [These are all birds that I have observed this year]. I understand that the lists display population trends and not actual population numbers, but I can not understand how the crossbill is on the green list with no recorded sightings in 2010 and the yellowhammer is on the red list with 1141 recorded sightings, and my own observations that there are significant numbers in this location, with several flocks of 20 to 30  birds being frequently seen on roadsides in autumn in this area.

I then looked up the full survey details [last full set that I could find being for 2010]. Some of the results that I saw  amazed me. For example, in 2010 I observed a flock of redwings that I estimated to be 50 to 60 birds and I frequently observed between 5 and 10 birds associated with larger flocks of fieldfares. Only 5 birds were recorded for the whole of England in the 2010 survey. I also observed a flock of in excess of 400 fieldfares when only 1157 in total were recorded in the survey.

The list where my own sightings exceed 1% of the recorded sightings goes on:-  8 tree sparrows - 773 recorded; 12 siskins - 294 recorded; 50+ sandmartins - 729 recorded; 2 rock dove - NIL recorded; 18 wigeon  [this year!] 66 recorded 2010; 4 crossbills [this year] 343 recorded 2010 . I can not believe that my area is so unique, containing such high proportions of these, and potentially of other species.,or is it that I am just completely misunderstanding the information provided in the bird population surveys? 

An idea of bird population numbers is important for developing strategies to help to sustain decreasing populations, but results such as those highlighted above make me wonder as to the accuracy of the estimations made from the surveys being carried out, and therefore any remedial actions, subsequently taken, based upon these results.

Can anyone explain 'in words of one-syllable' any of the points that I have tried to make here? It would be nice to be able to argue a point on populations and know that my information was supported by scientific fact, but this seems to be increasingly difficult when the evidence of my own eyes apparently contradicts the global scientific evidence.