Was the termination due to a tardiness that had occurred, say in the last few days? In other words, what it's going to come down to is "Having full knowledge that you were about to be terminated for tardiness, knowing that you had, according to company policy, had enough tardy issues that you knew it was going to result in your termination if you were tardy one more time, did you willfully and knowingly then have another tardy?
Since the company is saying they terminated you for tardiness, I do not see any advantage to you in trying to tell the ajudicator that you weren't in fact fired for tardiness, you were really fired for poor performance. Why would you be dumb enough to bring another possible misconduct issue into the discussion that the employer has not even brought up? They either can or can't prove that you were willfully and knowingly committing misconduct by being tardy in violation of company policy, or you were not.
"Fair and honest" is a beautiful idea, but in this situation, in unemployment law, we're not trying for the whole big picture of the moral issues of this company or your employment history. We are just trying to figure out if the company had a valid misconduct reason to terminate you. They chose exactly what they wanted to say was the reason they are terminating you. whether it's "honest and fair" or not doesn't matter. Is it a valid misconduct issue?
While it would have been easier for you to defend receiving unemployment if they had, in fact, terminated you for performance issues, if they don't say it, don't you mention it either. There is absolutely no benefit to your case to do so. If they ask why you went into the performance issue situation when you filed your claim, say, "I don't feel that I was really terminated for tardiness, since I had not had an incident of tardiness since...... I think the company tried to use tardiness as an excuse to get rid of me for other reasons." You do not need to go into whether or not you got merit raises, etc, unless you are asked about it.
Once they have committed to "We fired him because he was tardy" then they can't in later hearings or appeals, bring in, "...and oh, by the way, he was also a lousy performer, and he didn't meet our production quotas," They have to stick by whatever reason it was they gave when you were terminated.
They will be asked in detail about what the company policies about tardiness are. If they have those policies clearly stated in a handbook, and you were given the appropriate warnings in obedience to those policies, that's easy for them to document. If they do not have the policies clearly stated, and as you believe, they were not following any clear cut policy related to how many tardinesses are appropriate---or if they do not have a precipitating indicent of any kind, if they came up and said, 'Oh by the way, we are terminating you at this time for those tardiness incidents you had seven months ago" then you will have a strong possibility of getting approved.
But remember, no matter what is said, what is done in this initial hearing, either you or the employer can appeal this decision and then there will be the real official hearing. So don't get too excited about this one.