Runes on Armor
First in the future you should put questions like this in the Players Helping Players forum section, not only is that the right place but you are less likely to get insulted by trolls there.
As for your question the 1/4 represents that you can get bonuses for having up to 4 of that same rune in different pieces of armor not that the armor piece can hold 4 runes. Each armor piece can only hold a single rune but minor(up to 2), major(up to 4), and superior(up to 6) have bonuses for having multiple of the same rune in different armor pieces. The runes are designed to give better or more specific bonuses the more of the same kind you have in your armor.
To learn more about runes see the wiki entry for runes here: http://wiki.guildwars2.com/wiki/Runes
You replaced the original rune with another one. If you want bonuses for runes you need to have the same family of runes (i.e. pirates) and put them on each armor. If you put a rune on another rune it will replace it.
For e.g. If I want all four bonuses (4/4) for Pirates, I would need 4 runes on 4 out of the 6 armor pieces.
If you keep putting runes on 1 piece of armor you are just wasting gold and replacing the old rune.
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Howdy and welcome!
Without seeing exactly what runes you tried to add I am going to mention a possible issue.
Perhaps you didn’t use two of the same rune. They have to be the same rarity and type. You menttioned Pirate and you saud 1/4, which I think is Major. So all of the runes have to be “Major rune of the Pirate” to ge the number to increase. Anything else will not increase the number.
Also the runes have to be on different pieces of armor. I.e. one on helm and one gloves. Placing a rune on top of an existing one replaces the exististing. It does not add.
Again i hope this helped. If not perhaps someone else will chine in wih other ideas of what happened, or some extra details might help.