You have to remember the indentations make a difference.
Ulcer is the main term
stasis (venous)- see Varix, leg, with, ulcer [this would be WITH varicose veins]
without varicose veins I87.2
It's telling you there's two options for stasis, with or without varicose veins. In this case, if you have stasis (venous), the word "See" directs you to the code you should be using; it's not a suggestion, it's a direction. "Varix" is a varicose vein, so it's saying you need to look under that term to find your code. If you have stasis without varicose veins, then you use I87.2 because there's no linkage to Varix.
If you then look under Varix, leg, with, ulcer it shows as
Varix (lower limb) (ruptured)
leg
with
ulcer
then there are several options as to indicate the site. In other words, you'd read this as a varicose vein(s), in the leg, with an ulcer... it's not an ulcer with a varicose vein, it's a varicose vein with an ulcer. (if you read this out loud it might make more sense.
Both of these codes are in a block of codes described as "Diseases of veins, lymphatic vessels and lymph nodes, not elsewhere classified".
I87.2 is "Venous insufficiency (chronic) (peripheral)", not related to varicose veins.
I83.009 is "Varicose veins of unspecified lower extremity with ulcer of unspecified site". As previously mentioned, there's a direction "Use Additional code to identify severity of ulcer (L97.-)"
If the only information you have is "venous stasis ulcer", you need to look under the See look up because it's been defined by "venous". I83.009 describes varicose veins of an unspecified lower extremity with an ulcer with an unspecified site.
I83.0 requires a 5th character so that would not be a default code. You can choose from I83.00 (unspecified lower extremity), I83.01 (right lower), and I83.02 (left lower), but they all require a 6th character, so none of these would be default codes.
If there is no mention of varicose veins, then you wouldn't look under "Varix". Therefore you're left with only one option, I87.2.
Bottom line: You need to consider the etiology. That's where my statement "it's not an ulcer with a varicose vein, it's a varicose vein with an ulcer" comes into play.