You run a search with SOLR enabled for numbers present in some of the filenames and see no results. For example, a search for "99" didn't return the "T99V3DCW1D.jpg" result.
The issue is not related to the search term being fully numeric. With the MIN_GRAM_SIZE = 3, you cannot search with less than 3 characters with SolrDB Enabled. Ie with only 1 or 2 characters (digits in the example above), seeing no results is expected behavior; see the Predictive Search vs. Solr Search.
The search works once the number of digits/characters in the search is greater than or equal to MIN_GRAM_SIZE as defined in
/usr/etc/venture/var/solr.conf. You can always add a '*' to the end of the search term to be able to get results.
Note: any length search string works if Solr DB is disabled