何謂 "Matched Pair" Tubes

Hello everybody,

I got puzzled by the above term and hope that some of you can indeed tell me the true meaning of it.

For a pair of vacuum tubes to be "matched", does it mean that they give the same reading when put under the tester? OR "matched" in a sense that they are produced on the same date / lot?

Someone told me that if the pair of tubes are not "matched", you MAY have different sound quality from different channels. BUT even if the tubes are produced on the same date / lot, they can still give different readings from the tester. In that case, they will still produced different sound.

Please point out my mistakes as I am really an amatuer in electronics.  

my understand is that, it is electronically match (reading).

if both tube read 64/65 mean it is perfect match! if 1 tube read 64/66, the other read 66/68 it is still close match but not perfect match...

tube produce on same date may not match electronically....

actually it depend on tube type and the circuit, if your circuit using 1 tube for left, 1 for right then match is important. if your tube got 2 channel then 1 channel for right, 1 for left and the orther tube is for other circuit then not match also can. (some circuit 1 tube for input, 1 for output -2channel tube)
Correct me if i'm wrong.

A further question.  

By using a single tube reads 64/65, does it mean that (electronically or technically) there will be minor difference between left and right channel?