As mentioned by George Y., there's (technically) no "valid from" date. I had a look at my last visa (I have dozens of them), and there are actually two dates in a row:
ENTER BEFORE: 12AUG2018
ISSUE DATE: 12FEB2018
Real dates from my last visa. This was a six-month visa. As you can see, the expiry date (ENTER BEFORE) is exactly 6 months (and one day) after the ISSUE DATE, which makes the latter the date from which the visa is valid: as soon as the visa is produced, its validity starts.
As I said in a comment above, I was told several times by the travel agency I use for Chinese visas that the first date of travel you fill in on the form is to make sure there's enough time to get the visa (ie if you want to leave in 2 days, there might be a problem, as the processing time for French passports is 5 working days). And it is definitely not for later departures. "You want later, come later lah" I was told every time...
So all in all, I would say that if you want a visa with a later start date, you'll have to do it later. One solution came to me (as I might use it myself: I can get a one-year visa in France, but not in HK...). If your country allows two passports, leave one with family/friends, along with photo, form, etc. Have them apply for you (either directly or via a travel agency) in due time, and courier the passport to wherever you are.