Each of the examples above is grammatically correct, but with a slightly different meaning.
First, the question of "past" or "last" is less important, and it may depend on context. To me, "past" means specifically that each of the three years in question has already ended, whereas "last" might include the current year. Context is more important than the choice of words here.
The phrasing is more important. This is somewhat subjective, but to me the different prepositions indicate these connotations:
- "... in the past/last three years": Cash flows steadily improved during some interval of these years
- "... for the past/last three years": Cash flows started improving three years ago and never stopped
- "... the past/last three years": Same as "for", but a bit awkward to my ears
- "... during the past/last three years": Same as "in"
- "... over the past/last three years": Probably the same as "for", but now there is some ambiguity. "Over" could be a comparison between the current improved cash flow and that of the previous three years.
There seems to be some regional variation on this topic, so I will report from my AmE perspective.
In your particular example, either option would be understood to mean the same thing: the speaker works at some point during the course of each weekday (Monday, Tuesday, Wednesday, Thursday, Friday).
“From” would probably be omitted in either case as it is not needed to indicate a day range.
Generally speaking, I was always taught to indicate inclusive ranges with the word “through”. This generally has more application in studying mathematics, but could have an impact such as the following:
- Read up through chapter 3.
- Read up to chapter 3.
Receiving instruction #1 with no further clarification, I would read chapters 1, 2, and 3. Instruction #2, on the other hand, presents a quandary. It seems most likely that I’m supposed to read chapters 1 and 2, stopping when I reach the start of chapter 3, and that’s indeed what I would think if I were given no other hint as to the instructor’s wishes.
As you can see there’s a lot of iffiness here, so even among native speakers there is occasionally confusion and/or clarification. A misunderstanding such as the following would not be unheard of:
A: We’ll be on the boat Wednesday to Saturday next week.
B: So you’ll be back on land that Saturday?
A: No, we dock Sunday morning and we’re spending Sunday on the road.
As always, consider your audience and the context. Working those five days is such a common occurrence that neither word is likely to confuse anyone as to what you mean. In other cases, you may wish to add “inclusive” after the range to clarify that the whole of the end-limit you’ve named should be considered part of the deal.
Best Answer
In the abstract, "from" and "in" are nearly interchangeable in those two sentences from a strictly grammatical perspective (either could grammatically be used, although there would be different nuances in meaning). However, the usage you show "sounds" right" to a native speaker in terms of which of the two words to use for each case. That is because of what we would assume are the missing words behind the meaning:
The "from" would refer to the collection from which they were selected more than the time period explicitly mentioned. The time period defines the collection.
Here, "in" refers directly to the time period and means "during".
Note: there are various interpretations and word choices people might assume for the missing words. The point here isn't the literal choice of the missing words, but the general sense of why "from" and "in" seem logical. "From" would seem to refer to selecting from some collection defined by the last ten years, while "in" would seem to relate to the film becoming available during the last ten years (direct reference to the time period).