"Take something as read" - very old meaning of read?
If you find the phrase in the OED, (meaning P9 under 'read'), the earliest examples given are:
(1811) "Petitions.., all of which were taken as read, and ordered to lie on the table."
(1863) "Gentlemen, I presume that..we may regard the report of the directors to be taken as read."
In both of these the phrase is literal: assume, or pretend, that the documents in question have actually been read. I am sure that this is the origin of the more metaphorical expression.
According to the Word Detective the origin is from parliamentary bureaucratic procedures and the meaning is just literal.
Take it as read:
The Oxford English Dictionary defines “to take something as read” as “to treat (a statement, a subject, etc.) as if it has been agreed, without having a discussion about it; to take for granted.” The phrase, which dates back to the late 19th century, most often seems to be used to mean “to accept something as a given or as having already been stated and heard, in order to move on to other things” (“‘It’s really I who ought to say ‘sorry,’ you know. … ‘We’ll take it all as read,’ put in Miss Wilson hastily,” 1930). “Take it as read” is a way to fast-forward past a discussion that would be pointless, painful or redundant.
The roots of “take it as read” lie in parliamentary procedure, the conduct of meetings governed by Robert’s Rules of Order and the like. It is common, for instance, for members of a group to accept the minutes of previous meetings “as read,” meaning without objection, or to approve a resolution as presented (“read”) to the group without modification or the debate that would ensue.
The minutes of nearly every organization under the sun, to judge from a Google search, are riddled with the phrase “accepted as read” (“Dr. Fister moved that the August 4, 2006 minutes be accepted as read. Ms. LaVallee seconded the motion, and it passed unanimously,” Board of Dental Examiners, Augusta, Maine, 2006). In the slightly less formal form “take it as read,” the phrase then became a popular way to move a conversation swiftly past a bump in the road.
I am reasonably certain (though without written authority) that the origin of the phrase is political/legal. It is often the case (and almost invariably was in the past) that anything to be treated as evidence must be formally read out in the meeting/hearing/, partly to allow it to be challenged and partly so that it is included in the verbatim record. Where a long document is not disputed, it is only sensible to direct that it be taken as [having been] read. and a note about where to find it inserted in the minutes.