Well, as far as I can see, there's only one unknown value (Unknown13) in the structure data that could possibly qualify, and... it doesn't seem quite right. I sorted the structures on that value in descending order here:
[iD] CODE = U13 ; full name
[01] EYE = 100 ; Advanced Communications Center
[02] WEAP = 86 ; Weapons Factory
[13] AFLD = 86 ; Airfield
[15] NUK2 = 75 ; Advanced Power Plant
[07] FACT = 70 ; Construction Yard
[10] HPAD = 65 ; Helipad
[19] HAND = 61 ; Hand of Nod
[18] PYLE = 60 ; Barracks
[08] PROC = 55 ; Tiberium Refinery
[14] NUKE = 50 ; Power Plant
[21] FIX = 46 ; Repair Facility
[12] SAM = 40 ; SAM Site
[05] OBLI = 35 ; Obelisk of Light
[04] ATWR = 30 ; Advanced Guard Tower
[06] GUN = 26 ; Gun Turret
[03] GTWR = 25 ; Guard Tower
[00] TMPL = 20 ; Temple of Nod
[11] HQ = 20 ; Communications Center
[16] HOSP = 20 ; Hospital
[09] SILO = 16 ; Tiberium Silo
(after this are all civvie buildings and the tech center with value 2, the bio lab and oil pump with value 1, and the walls with value 0)