Recharging NiMH cells after long period (18 months) of self discharge
I do not expect these cells to be damaged. Contrary to Lithium based cells, which are indeed damaged when fully discharged, NiMh cells can handle this as long as they are not reverse charged.

Reverse charging can happen when the cells are used in for example a camera and one of the cells has less capacity. When it is empty it will be reverse charged while the other cells still provide current.

But you appear to have left the cells on their own so reverse charging cannot happen in this case. The cells just emptied themselves due to self-discharge.

Personally I would use my lab supply to "kick the cells into life" with 0.5 A of current for 10 seconds or so while measuring their voltage.

If you do not have a lab supply but you do have a "dumb" charger (one where it takes 10 hours or so to a full charge) you could try to charge the cells in that. Since such a charger does not check the cell's voltage but simply charges with a small current, the cells might become alive again after an hour.