There where some forms left in Gwoyeu Romatzyh and abbreviated spellings that I needed to investigate on.

• -m
  While in 'Mandarin Primer" Chao clearly states that men in 你們 turns to -m before labials (p. 123) I had yet to find a form where he actually employed this rule. It's actually just two pages ahead: "Woom bu.sh syhg ren; woo.men sh san'g ren" (p. 121). So before b, p, m, f -.men changes to -m.
• -tz
  Chao says that -tz is an abbreviation of -.tzy ("-.tzy (which we abbreviate as -tz)", 'A Grammar of Spoken Chinese', p. 36) while at the same time stating that its etymological background is tzyy ("suffix -tz (<tzyy)", p. 55). As he normally retains the etymological tone, it is unclear to me, why he doesn't do so in this case.