R Recursive + Lag for previous dependent value

I've been reading a lot about lag or accumulate but still can't figure out how do work on mine. I've worked out a simplified data of mine like below and also my attempt of workaround of this

library(tidyverse)
library(lubridate)

currDt = ymd(20211130)

polyData = structure(list(CCDATE = structure(c(18716, 18715, 18713, 18712, 8895, 18498, 18690, 18689, 18688, 18323), class = "Date"),
                          CRDATE = structure(c(19080, 18898, 18896, 18895, 18895, 18862, 19054, 19053, 19052, 18687), class = "Date"),
                          mREGNO = c("BBB", "BBB", "BBB", "BBB", "BBB", "BBB", "DDD", "DDD", "DDD", "DDD"),
                          SCHDRNUM = c(7711858, 7710223, 7709517, 7709318, 7709172, 7487762, 7686649, 7684567, 7683420, 7374917),
                          MCCDATE = structure(c(18686, 18686, 18685, 18684, 18864, 18467, 18662, 18661, 18660, 18294), class = "Date")),
                     row.names = c(NA, -10L),
                     class = c("tbl_df", "tbl", "data.frame"))

# sort accordingly for row processing next step
# by REGNO and latest CHDRNUM
polyData = polyData %>%
  arrange(mREGNO, -SCHDRNUM)

n = polyData %>%
  group_by(mREGNO) %>%
  tally() %>%
  ungroup() %>%
  summarise(n = max(n))

n = n$n

polyData_backUp = polyData

# get carried backward CCDATE minus 1 month
# first round is temporary create columns for later use
polyData = polyData %>%
  mutate(# temporary Keep for latest tran of every mREGNO
         Keep = case_when(is.na(lag(mREGNO)) ~ 1, # latest tran or data
                          mREGNO != lag(mREGNO) ~ 1, # latest tran of every mREGNo
                          TRUE ~ 0),
         
         # temporary Carried_MCCDATE for latest and second latest tran of every mREGNO
         Carried_MCCDATE = case_when(is.na(lag(mREGNO)) ~ MCCDATE, # latest tran of data
                                     mREGNO != lag(mREGNO) ~ MCCDATE, # latest tran of every mREGNo
                                     lag(Keep) == 1 ~ lag(MCCDATE), # if latest tran is ok then only carry backwards
                                     TRUE ~ currDt)) # temporary as at date

# keep calculate base on the updated info for every rows
for (i in 2:n) {
  polyData = polyData %>%
    mutate(Keep = case_when(is.na(lag(mREGNO)) ~ 1, # latest tran or data
                            mREGNO != lag(mREGNO) ~ 1, # latest tran of every mREGNo
                            CCDATE <= Carried_MCCDATE ~ 1, # previous CCDATE must have at least one month gap
                            TRUE ~ 0),
           
           Carried_MCCDATE = case_when(is.na(lag(mREGNO)) ~ MCCDATE, # latest tran of data
                                       mREGNO != lag(mREGNO) ~ MCCDATE, # latest tran of every mREGNo
                                       lag(Keep) == 1 ~ lag(MCCDATE), # if latest tran is ok then only carry backwards
                                       TRUE ~ lag(Carried_MCCDATE))) # if latest tran is not ok then will carry from carried
}

Basically columns from CCDATE to MCCDATE are the original data sorted by mREGNO and SCHDRNUM (Descending); Columns from Carried_MCCDATE to keep are the ideal result I would want.

The criteria is as below and I've worked it out in excel and have try lag in R but it doesn't work. The reason is because I need to take care of recursive formula at Carried_MCCDATE and another depending column together.

For this sample with this small, I manage to do it with a loop but is there anyway I can achieve this by using tidyverse? Because my actual data is a lot bigger.

The Carried_MCCDATE formula would be:
1) If first row of different mREGNO then = MCCDATE
2) If not first row and previous row's keep = 1 then = previous row's MCCDATE
3) Else = previous row's Carried_MCCDATE

Excel formula for cell F1 =IF(C2<>C1,E2,IF(G1=1,E1,F1))

The Keep formula would be:
1) If first row of different mREGNO then = 1
2) If CCDATE <= Carried_MCCDATE then = 1
3) Else = 0

Excel formula for cell G1 =IF(C2<>C1,1,IF(A2<=F2,1,0))

Please help and thank you very much in advance!!