Sorry Silvia ,i donāt think that is correct.
I think the answer to you questions is no in both instances. The 12/8 (6/4) and the 18/16
They are very different,
A time signature denotes the (standard notation) amount of notes allowed withing a barr.
6/8 = 6 1/8 notes will fill the time but if you change that to all triplets you will get more notes but the time remains the same.
you therefor then cannot add up all the notes like there are 18 16th and say it is 18 16 time because thats how many notes there are when you count them. play 3 but count (time) is still 2 for ALL triplets
The triplet allows an additional note to be played within the duration of that triplet, it does not increase the time.
The exact same applies to the 12/8 itās not 12/8 its still 4/4 but with triplets.
@Richard_close2u
Hi Richard, can you double check me on this please to make sure I have this correct, I dont want to get this wrong lol, you will be able to explain this to @Silvia80 better than this , please 
R
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To me 4/4 and 12/8 are two different things that have one thing in common which is they both have 4 pulses in a bar.
You can call a 12/8 a ā4/4 with tripletsā, that is fine, but it is a Rhythm that exists on its own and is something different from a 4/4, it has a different feeling when you listen.
And 12/8 is different from a 6/4 as well, what changes is where you put the accents and this changes the feeling of it, I guess.
Itās not to be given for granted though that Iām always able to feel and recognise it.
With Memory by B. Streisand for example I thought it was in 6/8 and fingerpicked it in 6/8ā¦but listen and re listen again and again, I felt it hadnāt the peculiar 6/8 feeling!! and in fact I found out it is in 12/8!
Now Richard @Richard_close2u we much need the help of a Music Teacher here (
ā¦magic wordā¦please 
)
ā¦and since Iām not, please Rachel take all my statements with a pinch of saltā¦weāre just trying to make sense and understand and learn.
Iām not able to say much about an ipothetic 18/16 Lol 
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I think this where the thing of keeping the arm moving helps. Initially I do need to count patterns like this but once my arm has learned the pattern then the counting can fall away. My other approach is to hum the rhythm and my arm (usually) follows.
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