A little difficult without all the original material to determine context. However ....

The EOS (and STODA) gradients in ERSA are determined analytically (ie by calculation) following periodic surveys by the contracted surveyor. Basically, the relevant geometric area is overlaid and the various obstacles (as surveyed) in the area are run through a simple trig analysis to figure slopes. For each case of interest, the worst (ie "most critical") obstacle will determine the published results.

Now, it follows that the published data can ONLY apply for the obstacle survey data on the survey date. Next time around, it is quite common to find that things have changed ... trees grow taller, someone put up a new bit of whatever which pokes up a bit higher than what was there before, etc., etc.

For Joe PIlot, you generally only have the ERSA data to help, so whatever is in the current edition is what you use. Mind you, you might find that the next issue (which is waiting in the wings until the issue data) may have revised data. If the revision is significant, you would expect that the airport authority would have had issued a NOTAM to cover the period until the next ERSA edition becomes valid.