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For comparison, I did a search using simply "4478", which returned 11 clue solutions (1a,5d,10a,13a,13d,14d,15a,16a,16d,19a and 24d). I also did a search using "ST4478" as the criteria. This returned 6 solutions (1d, 13a,2d,9a,18d,20a,25a ) Notice that only one solution was common to both searches i.e. 13a. In my opinion, this is a strange result for a modern search engine which would usually return all results with the search "4478" including the subset listed as "ST4478"
Moral : you need to search using both criteria
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