What Plain Text is
Plain text here means columns lined up with spaces, the way a command line tool prints a table.
Terminal output, log files, fixed-width exports from older systems.
What reStructuredText is
reStructuredText simple tables underline the header with equals signs and align columns with spaces.
Python documentation, Sphinx projects and anything on Read the Docs.
What changes when you convert Plain Text to reStructuredText
Two shapes are handled. If the same character positions are blank on every line, those gutters are treated as column boundaries, so values containing single spaces stay intact. Otherwise the lines are split on runs of whitespace.
The equals-sign rule under the header is what tells Sphinx the first row is a header. Without it the table renders as data with no heading.
What carries over from Plain Text to reStructuredText
reStructuredText can express everything plain text holds about a table, so this conversion is about shape rather than loss.
reStructuredText marks its header cells differently from its data cells, so the first row is written with that marker.
The identifier 007 comes out of the reStructuredText as 007. Reading it as a number would have made it 7, and an id that changes value is worse than one that stays text.
The role "Analyst, data" survives with its comma, in one cell rather than split across two. That is the first thing to check in any converted table, and the usual place a reStructuredText file goes wrong.
The quotes around Jonah "Jo" Pryce are left as a plain quote character in the reStructuredText.