Hi Jeffro. I thought of saying "Persia" instead of "Media-Persia" but I said the latter for the following reasons. (1) I think that a number of Christian books I've seen say "Media-Persia" (or Medo-Persia). (2) The book of Daniel says "the Medes and the Persians" and that wording made me wonder if a confederation (or alliance) of two countries were spoken of, namely of Media and Persia. However I think my wording might also be a holdover from the influence of WT literature I read since before age 10 which say "Medo-Persia". You are right though in saying that I should have said "Persia" instead. Daniel was probably speaking of ethic groups rather than kingdoms when he said "the Medes and the Persians".
Regarding your claim that "there is no reason the author of Daniel would refer to the fall of the ‘Roman empire’ that didn’t even exist yet", it depends upon the purpose of of why Daniel wrote the prophecy (or hypothetically why God gave him the vision and an angel interpreted it for him). If it were partly to convince people over the centuries (including those who would live in the time of the end) that that Jehovah God exists, that God influences world events, and that God foresees the future, then it would make sense to include a prediction about the Roman Empire. However if the prophecy was given to give hope to Jewish people living in 2nd century B.C.E., that harsh gentile domination over the Jews would very soon end, and that God would soon (in the 2nd century B.C.E.) establish a kingdom of his own over the world, then it wouldn't make sense to refer to the Roman Empire and to times centuries beyond 164 B.C.E..
Regarding your question of "Did you read the article I linked a few days ago?" in response to what I wrote (in the words which you quoted), the answer is as follows. When I made my comment I had stopped being confident that some Jews were using Daniel to calculate the arrival of the messiah in 26 C.E., 29 C.E., 30 C.E. or any similar year. Note that I included the phrase of "(assuming the WT's claim was correct)". As a result of what you had told me I had lost my confidence (in the idea of Jews making the calculation), but I said what I said so you would know why in an earlier post I said "about the year 30 C.E." instead of precisely "in the year 30 C.E.". I thought my post might give the wrong impression, so I tried to prevent that wrong impression from happening by also saying "(assuming the WT's claim was correct)".
I have not yet downloaded the PDF of the article you linked to about the 70 weeks prophecy. That is because when I went to the download site I noticed that it required me to provide my email address (or access with a Facebook sign in or a Google sign in), but I am hesitant to provide such information to that site. However, at some point I probably will do so, after I evaluate the site and/or read some agreement form (if any) pertaining to accessing the file from the site, in order to determine how the site will use my personal information. Update: Today I discovered it can be read it online if I click on the link which expands the document to show all of the pages online. But, I noticed it is many pages long and I am not yet interested in reading all of the pages. However, I intend to at least browse the pages when I have more free time.