This is listed as JLPT L2. However, it wasn't included in my L2 test book. I first saw it in my N1 grammar book.
What's the difference between this grammar and ~ても (~te mo)?
The 'た' can be from any past tense verb so it could equally be だ from 読んだ and such.
ところで also means "by the way" which you use in trying to change the subject. ところで、あの件はどうなったの？
updated. tnx. :)
#5505 has redundant kana? I have heard this grammar used a lot right at the point where the speaker gives up in a hopeless situation. Simlar to saying "Even if ... it's too late." The sentence usually ends in 〜ない or words such as 無理だ or 無駄だ。