It depends on what translators choose to use.
Ven. Thanissaro's translation of AN 8.26 says:
"Lord, to what extent is one a lay follower?"
Ven. Sujato's translation of AN 8.26 says:
“Sir, how is a lay follower defined?”
It turns out that the Pali sentence is:
“kittāvatā nu kho, bhante, upāsako hotī”ti?
In this case, the term "bhante" is translated as "lord" by Ven. Thanissaro and as "sir" by Ven. Sujato.
In this sutta (MN 147), "bhante" is translated as "venerable sir" by Ven. Bodhi.
Of course, "venerable sir" is the best translation.
Usually, the Buddha is addressed as "bhante" (venerable sir) in the second person and as "bhagava" (blessed one) in the third person.
This is in reference to Pali suttas.