Rules from the higher-ups forbid Marco from releasing engine numbers except under very specific circumstances.
FWIW, the records I've seen myself (for a very specific type of car) did not have any
information about engine numbers in them. During my visit at the archive, I got a clear sense that Alfa must have purged some records over time -- especially production records that were only for managerial use and/or internal communications or notes and annotations that not necessarily fell under accounting rules and regulations and/or laws for information retention for tax audits and legal liability.
It appears Alfa kept only a bare minimum of records on hand. for reference. However, I was told that there is also a room full of presumably mostly technical documentation that has never been cataloged. This became apparent when I asked Marco about a specific engineering drawing of an engine (of which I had seen a copy somebody had obtained from Alfa Romeo in the 1960s), and Marco told me that he does not know of any such drawing, but maybe it is in the room with uncataloged documents.
The big risk with the uncataloged documentation is that Alfa Romeo management may at some point in time decide to get rid of it, or some souvenir hunters or thiefs may extract some historically significant pieces, at which point history is lost because the documentation is not recorded and therefore does not exist officially.
One way or the other, I believe we have to thank Fusi that the Centro Documentazione even exists in its current form. I had the impression that Marco is fighting hard to keep serving Alfisti well even with the constraints management is putting on him that seem to make providing such services increasingly difficult.