Since + duration = interval or not?

[everzeni]

We had a few cases for which we couldn't really decide if they are intervals or values:

• the mechanical oscillator method is well established since about 2 decades
• Over the past three decades

We hesitated:

the mechanical oscillator method is well established since about <measure type="interval"><num atMost="2">2</num> <measure type="TIME">decades</measure></measure>
or
the mechanical oscillator method is well established since about <measure type="value"><num>2</num> <measure type="TIME">decades</measure></measure>

Over the past <measure type="interval"><num atMost="3">three</num> <measure type="TIME">decades</measure></measure>
or
Over the past <measure type="interval"><num atMost="3">three</num> <measure type="TIME">decades</measure></measure>

It seems to me that if we were to annotate those as intervals, we should bound them with the date corresponding to the beginning of the time periods. For examples 1998 for since about 2 decades, but it would be complicated to decide the starting point to compute the duration from... the publication of the article?

I think we should annotate them as atomic values, what do you think?