I'm afraid that the link you gave is a different situation. What they are saying there is that a new (i.e. changed functionality) vi can be used in place of an older (same version of LabVIEW) without 'relinking', which is a different animal than recompiling, if the connector pane hasn't changed. If you are trying to link vi's of a new version of LabVIEW to those of an older version, it will try and recompile them. If the older ones don't have diagrams this will fail. When you refer to your #2 and #3 vi's and talk about replacing them with newer ones, the mere act of reading them into a newer version will automatically either replace (built in labview functions) or recompile the ones you created, but it will require them to have diagrams. Depending on the level of effort to try and recreate the old code, the money the client is willing to spend, etc., you might look into one of the data recovery houses, they have performed some near miracles in data recovery, but they tend to price these miracles pretty expensively.
P.M.
PutnamCertified LabVIEW Developer
Senior Test Engineer North Shore Technology, Inc.
Currently using LV 2012-LabVIEW 2018, RT8.5

LabVIEW Champion