Different databases, there are several different databases inside the EI search, among which Compendex is the database of EI itself, its search number is 14 digits, starting with the year; and Inspec, the search number of this database is 8 digits.

When we say "indexed by EI", we mean indexed by Compendex, so the 14-digit number is correct.

Inspec, incidentally, is a database compiled by the Institution of Electrical Engineers of the United Kingdom, although the articles included in it can also be retrieved by the EI, but strictly speaking, it is not considered to be included in the EI, that is to say, "being retrieved by the EI" is not the same as "being included in the EI! In other words, "EI-retrieved" is not the same as "EI-included". Of course, there are many cases in which an article is included in both Compendex and Inspec, and according to what I said before, the 14-digit retrieval number of Compendex shall prevail.