Two common themes I've heard from instructors of yore, "every rule in this book came from some accident or incident," and " this book was written by lawyers."
Are the statements true? Who knows?
Do the statements make sense? Yes.
I believe a large number of changes came about after the Tenerife disaster. If you want to see a shocking transcript (by today's standards) of unclear and vague phraseology have a look at this:
KLM (Radio) Uh, the KLM ... four eight zero five is now ready for take-off ... uh and we're waiting for our ATC clearance.
1705:53.4
TENERIFE TOWER KLM eight seven * zero five uh you are cleared to the Papa Beacon climb to and maintain flight level nine zero right turn after take-off proceed with heading zero four zero until intercepting the three two five radial from Las Palmas VOR.
(1706:08.2) 1706:09.6 KLM (Radio)
Ah roger, sir, we're cleared to the Papa Beacon flight level nine zero, right turn out zero four zero until intercepting the three two five and we're now (at take-off).
(1706:17.9) 1706:13.0
KLM CAPTAIN We gaan. (We're going)
1706:18.19
TENERIFE TOWER OK.
1706:19.3
PanAm Radio(c/p) No .. eh.
1706:20.08
TENERIFE TOWER Stand by for take-off, I will call you.
1706:20.3
PanAm Radio(c/p) And we're still taxiing down the runway, the clipper one seven three six.
1706:19.39- 1706:23.19
RDO and TENERIFE TOWER communications caused a shrill noise in KLM cockpit - messages not heard by KLM crew.
1706:25.6
TENERIFE TOWER Roger alpha one seven three six report when runway clear
1706:29.6
PanAm Radio(c/p) OK, we'll report when we're clear.
TENERIFE TOWER Thank you
1706:32.43
KLM FLT ENGR Is hij er niet af dan? {Is he not clear then?}
1706:34.1
KLM CAPTAIN Wat zeg je? {What do you say?}
1706:34.15
KLM -? Yup.
1706:34.7
KLM FLT ENGR Is hij er niet af, die Pan American? {Is he not clear that Pan American?}
1706:35.7
KLM CAPTAIN Jawel. {Oh yes. - emphatic}
1706:40.0
PanAm captain sees landing lights of KLM Boeing at approx. 700m
1706:44.0
PH-BUF started rotation
1706:47.44
KLM CAPTAIN [Scream] 1706:50.0 collision