As far as Mackenzie's Nova Scotia version, I've found other of his "collected" versions that are also found in the Forget-Me Not songsters that are nearly identical to the Songster texts.
Here is what I call the "standard text" as found in the Roxburge and Deming broadsides that is found partially or wholly with variation in all traditional versions (Pretty Polly/Polly's Love etc.):
Standard Text Type A Roxburghe:
14. So with kind embraces he parted that night, She went to meet him in the morning light; He said, "Dear charmer thou must go with me, Before we are wedded, a friend to see."
15. He led her through valleys and groves so deep, At length this maiden began for to weep; Saying, "William, I fancy thou leadst me astray, On purpose my innocent life to betray."
16 He said, "That is true, and none you can save, For I all this night have been digging a grave." Poor innocent soul! when she heard him say so, Her eyes like a fountain began for to flow.
(This next stanza (17) where she begs for her life is standard but the reference to her child is usually missing. The last two lines of 17 are included except for "infant":
O pity [the infant], and spare my life, Let me go distress'd if I'm not thy wife.")
18. Her hands white as lillies in sorrow she wrung, Beseeching for mercy, saying, "What have I done To you my dear William, what makes you severe? For to murder one that loves you so dear."
19. He said, "Here's no time disputing to stand," And instantly taking the knife in his hand; He pierced her body till the blood it did flow, Then into the grave her body did throw.
20. He cover'd her body, then home he did run, Leaving none but birds her death to mourn;
Standard Text Type B: The Deming Broadside
12) With tender embraces, they parted that night, And promised to meet the next morning at light William said — Mary, you must go with me, Before we are married, our friends for to see.
13) He led her through groves and valleys so deep At length this young damsel began for to weep Crying William, I fear you will lead me astray On purpose my innocent life to betray.
14) He said you've guess'd right all earth can't you save For the whole of last night I've been digging your grave, When poor ruined Mary did hear him say so, The tears from her eyes like a fountain did flow
15) A grave with a spade lying near she did see, Which caused her to sigh and weep bitterly;
(Half of 15 and part of 16 are not standard. The text in brackets should not be part of the standard text)
16) Oh, pity [my infant] and spare my poor life, Let me live full of shame if I can't be your wife, Oh! take not my life, lest my soul you betray, [And you to perdition be hurried away].
17) Her hands white as lilies, in sorrow she wrung, Imploring for mercy, crying what have I done; To you dearest William, so comely and fair, Will you murder your true-love that loved you so dear?
18) He said, this is no time disputing to stand, Then instantly taking a knife in his hand-- He pierced her fair breast, whence the blood it did flow, And into the grave her fair body did throw.
19) He cover'd the body, and quick hastened home- Leaving none but the small birds her fate to bemoan:
(Some standard modified versions have him boarding a ship where he sets sail and the ship sinks- this is not part of the broadside text)