Again = 'back, opposite direction'

In the OED, archaic again, under def. 1a, is ‘In the opposite direction; back.’ The last example given there is from John Bunyan, with "turn again": "Come then, Neighbour Pliable, let us turn again, and go home."

But in def. 1b, there are a few quotes with "turn again", from the same 1612 source (def. 1b: "Back to or towards the point of starting; all the way back; = back adv. 5. Frequently with verbs of motion, such as bring, come, go, turn, wend. Now archaic (in continued use of the expressions illustrated in quots. 1611, 1612) and Scottish (north-eastern)."):

1612 R. Johnson Crowne-Garland Goulden Roses sig. Bvv
"London bells sweetly rung… Euermore sounding so, turne againe Whittington: For thou in time shalt grow, Lord Maior of London."

1846 C. Dickens Dombey & Son (1848) iv. 32
"Turn again Whittington, Lord Mayor of London, and when you are old you will never depart from it."

1983 V. E. Neuburg Pop. Press Compan. to Pop. Lit. 81/1
"He was inspired by hearing Bow bells ring out a peal which seemed to say: Turn again Whittington, Lord Mayor of London."

So, I’m wondering why the Bunyan quote isn’t in 1b, and if it is properly in 1a, then how is it different from the "turn again" 1b example(s)?