Wherever your station came from, some record of it probably exists: your own captures from Reef Demographer, an earlier cohort's work, a photograph somebody took because the reef looked nice. Almost none of it will meet this course's capture standard, because it was shot before anyone knew what would be wanted.
That is the ordinary condition of every long-term monitoring program. Knowing what such material is worth is the skill, not a consolation prize — and your own record will one day be the older data somebody else has to assess.
Without scale, an exposure reference and a known camera position, imagery cannot support cover percentages. It can often support plenty else: whether that colony is still there, whether it was obviously bleached or obviously broken, whether that overhang has collapsed.
What you owe is the audit, not the comparison. You find whatever prior imagery exists and state what it can and cannot support. A finding of none exists is complete and correct.
You do not edit it. An inherited record is never reformatted, corrected or re-scored. Your contribution is a separate dated Entry under your own name. The temptation to tidy is strong — the format is awkward, the class list is one you dislike, there is an error you are certain about — and it must be resisted, because correcting it destroys the record of who observed what, when, and how. That provenance is what lets a later reader judge any of it. A merged record with no provenance is worth less than two separate ones, because it looks authoritative and cannot be taken apart.
And here is the trap. The earlier record used a different class list, or fewer points. Your figures and theirs do not line up. The obvious fix is to re-score their images with your method, and then they match beautifully.
Do not. Run the governing test: re-scoring the old record to your method makes the two agree by construction, so the less the two methods had in common originally, the cleaner the agreement you manufacture. Wider uncertainty, stronger apparent agreement — the anti-conservative direction, wearing the clothes of diligence.
The correct move is the opposite. State the difference and narrow what the comparison supports. Coarser class list: compare at the coarser level. Fewer points: their uncertainty was wider and stays wider. And if the methods differ so much that nothing survives, that is a finding worth writing down. It tells the next person what not to change.