That's irrelevant. What's the point of analysing a sentence from the perspective of the time of quoting? You analyse it from the moment of utterance.
When "it has rained four times since October" was presented in the OP on 22-Jun-2019 at 16:38, it doesn't necessarily mean it was intended to be interpreted by reference to that time. A priori, it could have been uttered much earlier than that, as from some fictional work, but presented, or quoted, on 22-Jun-2019 at 16:38.
Let me make this clear: The word since sets only the beginning point of the timeframe within which the events happen. It does not tell you when the events happen. The first event could occur either at, or some time after, that beginning point of the timeframe.
But consider "There have been many changes since the war." Someone told me the changes had to occur
after the war.
What runs counter exactly? With the word after, the dictionary means exactly what I'm saying here—that the timeframe in question begins at that point.
I'm afraid the dictionary has more than one time-related definition for
since, and they don't specify the time frame in the same way. Merriam-Webster, for example, gives the following definition:
in the time after (a specified time or event in the past): from (a point in the past) until the present time
The first one is like Collins' "during or throughout the period of time after" and sets the beginning of the time frame after a time or event in the past. (One example would be "I haven't eaten since breakfast." )
Now consider "It has only rained once
since May." According to you, the time frame stretches from May 1 to the time at which the utterance was made. But if we plug Collins' definition "
during or throughout the period of time after" into the example, it means it could not have rained during the month of May, but during or throughout the period of time
after May. (N.B., Collins' example might not properly reflect the definition.)
Consider another example: John has seen Mary since 10 o'clock. It is taken to mean John saw Mary after ten.
Now compare that with "It has been raining
since May." The rain is interpreted as first occurring during the month of May, not after it. Therefore the above definition doesn't work here.
Look at this short dialogue:
A: How many cigarettes have you smoked since the beginning of the year?
B: Only one.
In the above exchange, person A is presenting to person B a timeframe stretching from January 1 until now within which to set any possible smoking events. All we know from B's response is that there has been one smoking event in that period, and we don't know at what point it occurred.
Maybe the definition at work here is "
from (a point in the past) until the present time." Which definition is relevant may have to do with the durative vs. punctual distinction of predicates.
