Is it expected behavior for StackExchange.com's "search all sites" to not return results that are returned using site-specific search? For example, I recently searched for the term "collider" three different ways:
StackExchange ("search all sites"): http://stackexchange.com/search?q=collider Returns sometimes no results, sometimes one result, which links to the High Energy Physics Area51 proposal, which has been deleted.
StackOverflow: https://stackoverflow.com/search?q=collider Returns 80 results.
CrossValidated: https://stats.stackexchange.com/search?q=collider Returns one result.
I believe "search all sites" uses a custom Google search, while the site-specific searches use Lucene, so some discrepancy is expected. For example, http://stackexchange.com/search?q=%22collider+bias%22 returns one result, but https://stats.stackexchange.com/search?q=%22collider+bias%22 returns no results, presumably because the search terms appear in a comment, which Google searches but Lucene ignores. However, in the original "collider" query, I would have expected "search all sites" to still return most of the results found on StackOverflow and CrossValidated.
Also, http://www.google.com/search?q=collider+site:stats.stackexchange.com returns two results, which are both missed by http://stackexchange.com/search?q=collider , even though (I think) the latter is also a custom Google search.
Are the above search results expected behavior? Generally, I like using the "search all sites" feature to find similar questions and answers on other SE sites. I imagine that there is a lot involved in searching and indexing behind the scenes that I am unaware of. However, in this case, I was surprised by how much was missed.