I managed to create my alarms correctly. To do this I first tried to modify the Tag Name field in the manager by adding _UPPER and _LOWER to the existing alarms but it did not work: the TagName field is updated in the ALARM table, but not in the PointTag field of the MEASUREMENT table that refers to it. Besides, I noticed that in this table the SignalID field of the existing measurement is included in the AssociatedMeasurementID field of the ALARM table for both the _UPPER signal and the _LOWER signal (unless it is the reverse; I can no longer verify). One of them refers to the 2 measurements ; the other refers to any.
I then proceeded to delete all the records from the ALARM and MEASUREMENT tables in relation to these alarms and have them properly recreated from Manager; taking care to add _LOWER and _UPPER to the Tag Name from the first recording (so that the PointTag of the Measurement table is identical to the TagName of the ALARM table, renaming wouldn’t work after this first record).
The automatic generation of the Tag Name being very practical, could I suggest to complete the current template [SEVERITY]: [SIGNAL] by adding at least [OPERATION]?
Indeed, there is no interest in setting the same severity for the same operation with a different alarm point. On the other hand, we will often have to position for the same severity on the same signal on different operations.
But that’s just a suggestion 
Anyway thank you for taking my remark into consideration.
Regards