The strata certificate of title is not just common property. Its a plan of all the property on that block of land.
The certificate of title of the lot does not carry any information related to the strata plan (ie there is no drawing on it) The certificate of title of a lot makes a reference to the strata title documents.
Remember that the Owners Corporation owns all of the land and buildings and a lot owns airspace and some walls.
The lines compose (usually) of thick lines denoting the building outline, Thin lines which are usually denoting boundaries outside of a building. They are always drawn perpendicular to the building. Dotted lines, denoting some physical feature (ie a bend in a fence line) that is not a boundary of a lot.
If there is confusion about the boundaries of a lot, I would seek the services of a surveyor who has good knowledge of the requirements of strata subdivision. They will at least be able to interpret the plan and provide some guidance.
It is a requirement of Land Registry Services that the strata plan defines the area of each lot or part lot. Since it a requirement it has to be on the plan. (That’s not a new requirement as I have seen it on 1970s plans) The strata plans are available from Land Registry Services through one of its agents. Maybe you do not have the complete number of pages (a strata plan extends over a number of pages even for small developments)