I assume from the above that the answer to my doubt
If, however, you can only read data for all your stocks, from outside, as an atomic operation, then some adjustments would be needed (it is still unclear to me which are your requirements).
is yes; you can only read updates for several or all stocks alltogether from a file. Then I'm afraid that the demo Data Adapter architecture is not suitable for you as a starting point.

What do you exactly read from your files?
Do you get values for all stocks or only for the modified stocks?
And, for each stock read, do you get values for all fields or only for the modified fields?

Dario