There is no 6 year saving cert, do you mean the 6 year installment savings ?
If so, you save for a year and the money stays put for another 5 years ( 6years in total)
You don't add money in year 2-6.
If you choose to open another one every year, then it works like this
Installment saving account 1 - Save in 2021, matures in 2026
Instlallment saving account 2 - Save in 2022, matures in 2027
These would be completely separate products with no link between them