Graph performance Index

Most of times when you set the graph performance index to the “first purchase” most of your holdings do not date back to that time (lets call it T0 time).
It seams to me, you tell me if i’m wrong, that that graph forces the value of the whole holdings of your portfolio combined to their value at that T0 date, even if you didn’t actually had those securities at that time.
As a consequence, the performance it shows let’s say from 10.000 points in T0 to 12.000 today is…false?
If so, this means that graph means basically…nothing. Not to say it is misleading…
Am I wrong? May be there is one other interpretation to it?

Moreover, the benchmark performance do not takes into account the adjustment of invested capital that occur in your portfolio…so it’ performance is not weight averaged as your portfolio is, and so its not comparable in the % performance displayed nor in the Graph performance Index.