Sirius' High - Security Vault? (Vaults 711 and 713)

[sixhoursahead <sixhoursahead@yahoo.com>]

No: HPFGUIDX 52282

Sorry for the double post.

While re-reading POA for the umpteenth time, I was struck by a small 
detail which I had not noticed before (if this has been brought up, I 
apologize, I did TRY to search the archives for it.)  In the letter 
Pig delivers to Harry from Sirius, Sirius explains how he gave Harry 
the Firebolt, and says that his vault is number 711.  

Isn't Sirius'vault number an extremely inconsequential detail?  Why 
is placed in there?  We never even know Harry's vault number, or hear 
the Weasley's vault number called out by a Gringott's goblin.  The 
only other vault we hear about is vault 713.  Am I the only one who 
is struck by the fact that these two vaults are practically side by 
side?  It leads me to believe that Sirius' personal vault is also, 
for some unknown reason, a high - security vault.  Now you may say, 
just because the are near each other, does not mean they are both 
high-security.  Maybe high-security vaults are spread out all over 
the place, but:
  1) Here is the passage where Hagrid, Harry, adn Griphook leave 
Harry's vault and continue onto 713: "They were going even deeper now 
and gathering speed.  The air became colder and colder as they 
hurtled round tight corners.  They went rattling over an underground 
ravine...Vault 713 had no keyhole."   I think this gives the 
impression that the high-security vaults are actually deeper or 
farther away or in a more maze-like area of the bank.  

  2) Why mention Siruis'vault number?  Why have it be vault number 
711?  We know what Sirius was doing before he was imprisoned, about 
as well as we know what Lily and James did for a living.  Will this 
become significant down the road?  

ANGELA