[OSM-talk] offering adapted databases

[Anthony]

This is an except from a message I sent to Steve.  But hopefully
someone can answer these questions for me (and for everyone who wants
to comply with the ODbL):

"If you publicly use any adapted version of this database, or works
produced from an adapted database, you must also offer that adapted
database under the ODbL."

How long do I have to keep a copy of the adapted database in case
someone takes me up on my offer?  How much of the database do I need
to keep?  Is the offer valid to third parties?  If person A makes a
bunch of tiles from a database, and person B prints out a map from
those tiles and gives the map to person C, who offers person C the
copy of the adapted database?  (Person B likely doesn't have a copy,
but Person A would have to keep a ton of obsolete data indefinitely if
his offer is valid to third parties.)

As of right now I have produced hundreds of thousands of tiles from a
myriad of different versions of a myriad of different databases.  If
someone asked me to give them a copy of the adapted database, I
couldn't possibly comply.