Inconsistency of reading addresses of holding registers base-1 vs base-0

[an3l]

I tried experimenting with Schneider PM2200
Modbus register list is here.
There are couple of problems when using this library:

• Wrong address compared to vendor register address list - base-1 vs base -0 addressing setup:
  Based on register list on address 1837 should be year, however I fetch the year information using this library from address -1 (1836) - so it means library is not reading correctly according to the specification:
  logger.info(master.execute(1, cst.READ_HOLDING_REGISTERS, 1836, 1))

2021-04-24 12:54:08,434 INFO    modbus_rtu.__init__     MainThread      RtuMaster com3 is opened
2021-04-24 12:54:08,449 INFO    rtu_master_example_anel.main    MainThread      connected
2021-04-24 12:54:08,449 DEBUG   modbus.execute  MainThread      -> 1-3-7-44-0-1-68-183
2021-04-24 12:54:08,496 DEBUG   modbus.execute  MainThread      <- 1-3-2-7-229-123-255
bytearray(b'\x03\x02\x07\xe5')
2021-04-24 12:54:08,497 INFO    rtu_master_example_anel.main    MainThread      (2021,)

Using the address (from vendor register list - 1837) I have read from Matrikon OPC client and got correct value, where 1836 address is also correct reading (cause of last meter reading - value from 0-2):

Is there any way to say the script which addressing we are using ?

• Reading string value:
  Based on that register list on address 50 (holding register) should be meter model (in utf-8). Because of previous problem with wrong address on address 49 I read the string, but bytearray() has a argument of char where struct.unpack() breaks - I will raise PR based on this.
  logger.info(master.execute(1, cst.READ_HOLDING_REGISTERS, 49, 3,data_format='>s'))
• Reading the float values:
  P.S. Not sure is this related to Problem with holding registers encoded as float #93
  Again shift in address - on address 2017 (instead of 2018) I can read the value (nominal voltage 230.0 V):
  logger.info(master.execute(1, cst.READ_HOLDING_REGISTERS, 2017, 2, data_format='>f'))

2021-04-24 12:54:08,551 DEBUG   modbus.execute  MainThread      -> 1-3-7-225-0-2-149-73
2021-04-24 12:54:08,600 DEBUG   modbus.execute  MainThread      <- 1-3-4-67-102-0-0-15-168
bytearray(b'\x03\x04Cf\x00\x00')
2021-04-24 12:54:08,601 INFO    rtu_master_example_anel.main    MainThread      (230.0,)

Using Matrikon OPC client on correct address (2018) I cannot see the value (where on 2017 is the again correct value- frequency of 50Hz). Note: when adding the 2018 address tag quality of frequency data is wrong, while when showing only 2017 address it ok (what may be something related to Matrikon reading of floats).