This is not strictly true, as words could also have -i, or -es, or if it has a double vowel in the word, these might change to another double vowel or two different vowels.
Just s, es, if there is y then remove Y and add ies after it
No, for proper names that end in 'y', only add an 's', for example the two Percys.The plural possessive form is the Percys'.
Its Rocky with a 'y' not 'ie', 'ie' is plural but you just have to add the 's': 'ies'; Rockies-(plural) Rocky- (normal not plural)
You don't drop the 'y' you just add 's' to make the plural monkeys.
Take off the -y and add -ies: documentaries.
Valleys ... because if the noun ends in y + a,e,i,o,u ( a vowel letter) as in boy (y+o) you do not cross out the y and add ies, you only add (s): boy+boys.... day =days, BUT if the noun ends in y+ a consonant letter (b,c,d....), we cross the (y) and add "ies", as in baby=babies... lady=ladies
it depends on the verb. It could just use an s, or ies.
because fly has a consonant before the y and boy has a vowel
The plural for pulley is pulleys. The rule for making nouns ending with 'y' plural is: If the 'y' is preceded by a vowel, add 's'. If the 'y' is preceded by a consonant, drop the 'y' and add 'ies'.
because its a grammatical affectation from the spelling police?
The general rule is to add "es" to nouns ending in s, x, z, ch, or sh to form their plural form. For other nouns, you typically add just an "s" to form the plural. However, there are exceptions, so it's important to consult a dictionary when in doubt.
To change a singular noun to its plural form, add -s, -es, or -ies to the end of the word, depending on the spelling rules. Make sure to adjust any accompanying verbs and pronouns to agree with the new plural form.