Don't remember "Mirroring"
Mirroring was probably adapted from standard cartomancy, especially as it evolved from Etteilla. It was known as "pairing" from the ends of a line or horseshoe-shaped layout. (Since we read Lenormand in "pairs" differently, the term mirroring is clearer.)
Knighting seems to be one of the more recent additions, which I believe was a short-cut or simplification for "counting in every direction" from the Significator - a cartomantic technique. Counting becomes confusing because people use a different number of counts and what "every direction" means could be almost anything. Knighting standardizes this, although some people also use a system of counting, too.
Houses are also adapted from a French cartomancy technique that first appeared (as far as we know) in 1875 in L'Oracle Parfait ou le Passe-Temps des Dames: Art du Tirer Les Cartes. It came to be known as "Lenormand's Nines" as one would lay playing cards from a 36-card deck in a 4x9 layout and then interpret each card according to the individual meanings given in the book for each card in each "house." Each house had a single word designation that does not correspond to the Lenormand cards (although there are enough similarities to make it usable). The original playing card technique can be found in English cartomancy books by Prof. Foli and Charles Platt. Erna Droesbeke uses Houses in her 1987 Dutch cartomancy book "Kaartleggen met Mlle. Lenormand" using the original "Lenormand's Nines" for the Houses. (Each card has 36 different meanings depending on the house in which it lands - so you need the book to look up each of these meanings.)
Yes, I think it's best to get really good with just a couple of techniques and then occasionally try out one of the others. Eventually you'll develop your own style of reading that really works for you. Trying something different can be refreshing if you are feeling stuck or stale.
